The art of preparing ophthalmic lenses from glass or plastic blanks entails edging blank lenses. Edging means that an ophthalmic lens is ground to a desired peripheral shape to fit a preselected frame. Additionally, during edging, the peripheral edge surface of a given lens may be beveled or otherwise profiled to cooperate with a reciprocal shape or an interior peripheral surface of a frame in order to hold the lens within the frame, to align with or support an edge seal applied to the lens, or for other purposes. Techniques and devices for edging ophthalmic lenses are well known in the art. See, for example, U.S. Pat. No. 4,179,851.
The formation of a composite eyeglass lens by bonding front and rear lenses together is also known. See, for example, U.S. Pat. No. 5,399,227. The '227 bonding process involves placing an adhesive on the concave surface of a first lens, pressing the convex surface of a second lens against the adhesive on the front lens to evenly spread the adhesive between the lenses and curing the adhesive to bond the lenses together. This process forms a composite lens which is then edged to fit within an eyeglass frame and which may be further processed if desired. U.S. Pat. No. 4,287,018 discloses a method for edging glass-plastic laminated lenses at elevated temperature. In this method, edging occurs after lamination.
Recently, laminated electrochromic lenses have been described. These lenses comprise bonded first and second complementary lenses and at least one thin film of a persistent electrochromic material, i.e., a material which, in response to application of an electric field of given polarity, changes from a high-transmittance, non-absorbing state to a low-transmittance, absorbing or reflecting state. The first and second lenses are complementary in that their mating surfaces are sized and shaped so that, absent alignment problems, spacing between the lenses after lamination is substantially uniform.
Since the degree of optical modulation is directly proportional to the current flow induced by the applied voltage, electrochromic lenses demonstrate light transmission tunability between high-transmittance and low-transmittance states. In addition, these lenses exhibit long-term retention of a chosen optical state, requiring no power consumption to maintain that optical state. Optical switching occurs when an electric field of reversed polarity is applied.
To facilitate the required ion and electron flows, an electrochromic film, which is both an ionic and electronic conductor, is in ion-conductive contact, preferably direct physical contact, with an ion-conducting material layer. The ion-conducting material may be inorganic or organic, solid, liquid or gel, and is preferably an organic polymer which also serves as a laminating agent. The electrochromic film(s) and ion-conductive material are disposed between two electrodes, which in turn are disposed between two lenses, forming a laminated cell.
When the electrode adjacent to the electrochromic film is the cathode, application of an electric field causes darkening of a cathodically-coloring film. Reversing the polarity causes electrochromic switching, and the film reverts to its high-transmittance state. Typically, an electrochromic film such as tungsten oxide is deposited on an ophthalmic lens coated with an electroconductive film such as tin oxide or indium tin oxide to form one electrode. The counter electrode is typically a similar tin oxide or indium tin oxide coated ophthalmic lens.
As voltage is applied across the electrodes, ions are conducted through the ion-conducting material. To ensure reliable operation, the ion-conducting material layer generally must be sealed so as to maintain its water content within a range sufficient to provide required ion conductivity. Absent an adequate seal, moisture loss or gain through the exposed edge of the ion-conducting material layer impacts performance. The peripheral edge surface of a laminated device may be shaped to support or interlock with an edge seal. For example, copending U.S. patent application Ser. No. 08/996,064, filed Dec. 22, 1997, discloses a nubbed-edge design that facilitates application of an edge seal to the peripheral edge surface of an electrochromic device. Because such nubs preferably comprise a raised portion of each of the lenses forming the laminate, accurate edging is essential.
A typical laminated electrochromic lens comprises a first electroconductive material layer which serves as a first electrode, an electrochromic layer, an ion-conducting material layer and a second electroconductive layer which serves as a second electrode. Preferably, a complementary electrochromic layer is also used. These electroconductive and electrochromic layers, along with the ion-conducting material layer, can be arranged as a single stack deposited on a first lens which is then laminated to a second lens, or they can be arranged such that the electrodes are coated on separate lenses, followed by placement on the lenses of one or more electrochromic layers. The coated lenses are then laminated via a technique which positions an ion-conducting material between the coated lenses. Preferably, an ion-conducting polymer, which also serves as a bonding agent, is used to bond the complementary lenses.